The way I was taught: Fahrenheit sent his new thermometer with an
assistant to the far north to find the coldest temperature and mark the
thermometer at zero.

What I was taught (it may well be only half right) is that zero is the
freezing point of salt water (as salty as possible) and that 100 is body
temperature (he got that wrong). To the first part, it's why "below
zero" is significant - salt won't help on the roads.

0.5 ml per gallon for
80, and 2.0 for 100LL. Metric per U.S.

ml is a common small unit, and gallon is a common large unit, especially
in the context of gasoline.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.